In recent years, there have come into widespread use container closures in which a tear-off weakened line leading from a tear-off tab projecting from the skirt portion to the top surface of a closure is provided in the closure body so as to permit simple opening by pulling the tear-off tab. Since a considerable force must be exerted in pulling up the tear-off tab in opening a container closure of this type, measures have been taken to make the opening easy by providing a long tear-off tab, or by attaching suitable gripping piece. These measures, however, have the defect that many wastes are generated in the pre-shaping of a container closure from a thin metal strip, and therefore the cost of the closure increases.
Many methods have also been proposed for separately producing a gripping piece and connecting it to the tear-off tab by such means as bonding, rivetting or scissoring hold. These methods, however, have the disadvantage that much labor and time are required during the manufacturing process, the connecting portion is weak and causes troubles such as breaking before opening, and moreover the cost of production markedly increases.
In order to overcome these problems, Wicanders AB of Sweden has developed and filed patent applications No. 13855/1983 and No. 13856/1983 in Japan for a method and an apparatus therefor, of producing a container closure equipped with a metallic pull ring on a mass production basis at low cost which comprises forming an annular article having both ends overlapping each other by cutting a rectangular metal blank from the end portion of a thin metal strip and simultaneously bending it, positioning the annular article and a container closure such that a free end portion of a tear-off tab of the closure and a part of the annular article may overlap each other, curling the peripheral edge of the annular article in the radial direction to form a ring and simultaneously rolling the tear-off tab into the ring to connect them to each other.
This type of container closure equipped with a metallic pull ring, for example, has a structure as shown in FIG. 1. This container closure can be continuously shaped by an apparatus which is comprised basically of (1) a pre-shaped article forming means for cutting a thin metal strip to form an annular pre-shaped article, (2) a pre-shaped article feeding means for feeding the pre-shaped article to a position at which it is in communication with a tear-off tab of the closure, (3) a closure feed means and (4) a pull ring shaping and connecting means for shaping the pre-shaped article abutting against the tab of the closure into a pull ring and simultaneously connecting it to the closure.
In order to obtain a closure equipped with a metallic pull ring having stable quality at low cost, it is necessary to shape the annular pre-shaped article at sufficiently high speeds into a pull ring to connect it to a tear-off tab of the closure securely.